In the completion of hydrocarbon wells, it is known to use screens to prevent the production of solids from the formation. Expandable tubular technology has been used to expand metal screens to reduce the annular space around the screen and thereby reduce or eliminate the requirement for gravel packing and provide structural support for the formation.
There are a number of drawbacks to using expanding tubulars. It can be difficult to control the force used to expand the tubular, and there may be resulting problems with the application of an undue, damaging force onto the formation. Expandable tubulars also have a limited expansion range, which means that maximum expansion can still result in an unsupported formation in a wash out zone.
US 2005/0173130 describes an arrangement in which a swellable layer is located over an expanding screen to allow the apparatus to conform to the borehole shape. Holes in the swellable layer allow the passage of formation fluids. However, it is desirable in many applications to avoid the use of expanding tubulars. Additionally, by providing the screen around the expandable pipe at a location displaced from the borehole wall, there is an annular space into which solids may be produced, and along which solids may flow. This increases the risk of blocking the screen and creating so-called hotspots which are prone to erosion.
The proposal of WO 2006/003112 attempts to overcome these deficiencies by providing a screen which is expanded into contact with the borehole wall by swellable rings. This approach relies on overlaid screen sheets which are forced outward by the swelling of the rings. This has the undesirable effect of restraining expansion of the swellable material, which may only be capable of exerting a pressure of 50 to 100 PSI (345 to 690 KPa). In addition, the gaps between overlaid screen sheets provide route for solid particles to enter the production tubing.